FS#2108 - Support local language when install Flyspray

1. Web browser will setup "Accept-Language" header when request url. So, install program should parse this variable 'HTTP_ACCEPT_LANGUAGE' in $_SERVER, and load lang/LOCAL.php file first. It must call load_translations() in setup/index.php.

2. Some strings are hard code in setup/templates/*.tpl files, that should replace with " <?php echo Filters::noXSS(L('library'));" or "<?php echo L('library');". For example: